<meta charset="utf-8">
<title></title>
<table border="1">
<td colspan="4"><input id="result"> </td>
<tr>
<td><button onclick="s1()">1</button></td>
<td><button onclick="s2()">2</button></td>
<td><button onclick="s3()">3</button></td>
</tr>
<tr>
<td><button onclick="s4()">4</button></td>
<td><button onclick="s5()">5</button></td>
<td><button onclick="s6()">6</button></td>
</tr>
<tr>
<td><button onclick="s7()">7</button></td>
<td><button onclick="s8()">8</button></td>
<td><button onclick="s9()">9</button></td>
</tr>
<tr>
<td><button onclick="s0()">0</button></td>
<td><button onclick="dian()">.</button></td>
<td><button onclick="add()">+</button></td>
</tr>
<tr>
<td><button onclick="jian()">-</button></td>
<td><button onclick="cheng()">*</button></td>
<td><button onclick="chu()">/</button></td>
</tr>
<tr>
<td><button onclick="dengyu()">=</button></td>

<td colspan="2"><button onclick="qingling()"></button></td>
</tr>

</table>

<script>
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   var n2;
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 function s3(){ 
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 function s4(){ 
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 function s5(){ 
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    }
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    }
 function s7(){ 
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    }
 function s8(){ 
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    }
 function s9(){ 
       result.value=result.value+9;
    }
 function s0(){ 
       result.value=result.value+0;
    }
 function dian(){ 
       if(result.value.indexOf(".")==-1)
  {
           result.value = result.value + ".";
 }
    }
  function add(){ 
      n1=parseFloat(result.value);
 
       result.value="";
       n2="jia";
    }
  function jian(){ 
      n1=parseFloat(result.value);
 
       result.value="";
       n2="jian";
    }
function cheng(){ 
      n1=parseFloat(result.value);
 
       result.value="";
       n2="cheng";
    }
function chu(){ 
      n1=parseFloat(result.value);
 
       result.value="";
       n2="chu";
    }
  function dengyu(){ 
       if(n2=="jia"){
           result.value=n1+parseFloat(result.value);}
       if(n2=="jian"){
           result.value=n1-parseFloat(result.value);}
      if(n2=="cheng"){
           result.value=n1*parseFloat(result.value);}
     if(n2=="chu"){
           result.value=n1/parseFloat(result.value);}
   
    }
function qingling(){ 
      
       result.value="";
       
    }
</script>